#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb/stb_image.h>

#include "core/Shader.h"

#include <iostream>
#include <algorithm>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include "core/Camera.h"
#include <random>
#include "model/Model.h"

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow* window);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
unsigned int loadTexture(char const* path, bool gammaCorrection, bool bFlipV);
void renderCube();
void renderQuad();

// basic settings
const unsigned int SCR_WIDTH = 800, SCR_HEIGHT = 600;
float deltaTime = 0.0f; // 当前帧与上一帧的时间差
float lastFrame = 0.0f; // 上一帧的时间

// camera
Camera camera = Camera(glm::vec3(-0.263483, 3.21759, 10.4436), -89.7, -18.1);
float cameraNearPlane = 0.1f;
float cameraFarPlane = 500.0f;
float lastX = 400, lastY = 300;

// render var
unsigned int quadVAO = 0, quadVBO = 0;
unsigned int cubeVAO = 0, cubeVBO = 0;

unsigned int gScrrenTextureIndex = 4;
bool bToggleGBufferKeyPressed = false;
bool bRenderSpecular = false;

const unsigned int NR_LIGHTS = 32;

int main()
{
	// glfw: initialize and configure
	// ------------------------------
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

	// glfw window creation
	// --------------------
	GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
	if (window == NULL)
	{
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
	glfwSetCursorPosCallback(window, mouse_callback);
	glfwSetScrollCallback(window, scroll_callback);

	// tell GLFW to capture our mouse
	glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

	// glad: load all OpenGL function pointers
	// ---------------------------------------
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}

	// configure global opengl state
	// -----------------------------
	glEnable(GL_DEPTH_TEST);

	// build and compile shaders
	// -------------------------
	Shader gBufferShader("shader/gbuffer.vert", "shader/gbuffer.frag");
	Shader screenShader("shader/screen.vert", "shader/screen.frag");
	Shader lightingPassShader("shader/lightingPass.vert", "shader/lightingPass.frag");
	Shader lightBoxShader("shader/shader.vert", "shader/shader.frag");

	Model backpack("backpack/backpack.obj");
	std::vector<glm::vec3> objectPositions;
	objectPositions.push_back(glm::vec3(-3.0, -0.5, -3.0));
	objectPositions.push_back(glm::vec3(0.0, -0.5, -3.0));
	objectPositions.push_back(glm::vec3(3.0, -0.5, -3.0));
	objectPositions.push_back(glm::vec3(-3.0, -0.5, 0.0));
	objectPositions.push_back(glm::vec3(0.0, -0.5, 0.0));
	objectPositions.push_back(glm::vec3(3.0, -0.5, 0.0));
	objectPositions.push_back(glm::vec3(-3.0, -0.5, 3.0));
	objectPositions.push_back(glm::vec3(0.0, -0.5, 3.0));
	objectPositions.push_back(glm::vec3(3.0, -0.5, 3.0));

	// configure g-buffer framebuffer
	// ------------------------------
	unsigned int gBuffer;
	glGenFramebuffers(1, &gBuffer);
	glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
	unsigned int gPosition, gNormal, gAlbedoSpec;
	// position color buffer
	glGenTextures(1, &gPosition);
	glBindTexture(GL_TEXTURE_2D, gPosition);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, gPosition, 0);
	// normal color buffer
	glGenTextures(1, &gNormal);
	glBindTexture(GL_TEXTURE_2D, gNormal);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, gNormal, 0);
	// color + specular color buffer
	glGenTextures(1, &gAlbedoSpec);
	glBindTexture(GL_TEXTURE_2D, gAlbedoSpec);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT2, GL_TEXTURE_2D, gAlbedoSpec, 0);
	// tell OpenGL which color attachments we'll use (of this framebuffer) for rendering 
	unsigned int attachments[3] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
	glDrawBuffers(3, attachments);
	// create and attach depth buffer (renderbuffer)
	unsigned int rboDepth;
	glGenRenderbuffers(1, &rboDepth);
	glBindRenderbuffer(GL_RENDERBUFFER, rboDepth);
	glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT);
	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rboDepth);
	// finally check if framebuffer is complete
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "Framebuffer not complete!" << std::endl;
	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// configure light-pass framebuffer
	// ------------------------------
	unsigned int lightingPassFBO;
    glGenFramebuffers(1, &lightingPassFBO);
    glBindFramebuffer(GL_FRAMEBUFFER, lightingPassFBO);
	unsigned int lightingPassColorBuffer;
    glGenTextures(1, &lightingPassColorBuffer);
    glBindTexture(GL_TEXTURE_2D, lightingPassColorBuffer);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, lightingPassColorBuffer, 0);
	unsigned int lightingPassDepthBuffer;
    glGenRenderbuffers(1, &lightingPassDepthBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, lightingPassDepthBuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, lightingPassDepthBuffer);
	// finally check if framebuffer is complete
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "Framebuffer not complete!" << std::endl;
	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// lightingPass info
	// -------------
	std::vector<glm::vec3> lightPositions;
	std::vector<glm::vec3> lightColors;
	srand(13);
	for (unsigned int i = 0; i < NR_LIGHTS; i++)
	{
		// calculate slightly random offsets
		float xPos = static_cast<float>(((rand() % 100) / 100.0) * 6.0 - 3.0);
		float yPos = static_cast<float>(((rand() % 100) / 100.0) * 6.0 - 4.0);
		float zPos = static_cast<float>(((rand() % 100) / 100.0) * 6.0 - 3.0);
		lightPositions.push_back(glm::vec3(xPos, yPos, zPos));
		// also calculate random color
		float rColor = static_cast<float>(((rand() % 100) / 200.0f) + 0.5); // between 0.5 and 1.0
		float gColor = static_cast<float>(((rand() % 100) / 200.0f) + 0.5); // between 0.5 and 1.0
		float bColor = static_cast<float>(((rand() % 100) / 200.0f) + 0.5); // between 0.5 and 1.0
		lightColors.push_back(glm::vec3(rColor, gColor, bColor));
	}

	// shader configuration
	// --------------------
	lightingPassShader.use();
	lightingPassShader.setInt("gPosition", 0);
	lightingPassShader.setInt("gNormal", 1);
	lightingPassShader.setInt("gAlbedoSpec", 2);
	// send light relevant uniforms
	for (unsigned int i = 0; i < lightPositions.size(); i++)
	{
		lightingPassShader.setVec3("lights[" + std::to_string(i) + "].Position", lightPositions[i]);
		lightingPassShader.setVec3("lights[" + std::to_string(i) + "].Color", lightColors[i]);
		// update attenuation parameters and calculate radius
		const float linear = 0.7f;
		const float quadratic = 1.8f;
		lightingPassShader.setFloat("lights[" + std::to_string(i) + "].Linear", linear);
		lightingPassShader.setFloat("lights[" + std::to_string(i) + "].Quadratic", quadratic);
	}

	screenShader.use();
	screenShader.setInt("screenTexture", 0);

	// render loop
	// -----------
	while (!glfwWindowShouldClose(window))
	{
		std::string title = "LearnOpenGL";
		std::string renderTextureState;
		if (gScrrenTextureIndex == 0)
		{
			renderTextureState = "Position";
		}
		else if (gScrrenTextureIndex == 1)
		{
			renderTextureState = "Normal";
		}
		else if (gScrrenTextureIndex == 2)
		{
			renderTextureState = "Diffuse";
		}
		else if (gScrrenTextureIndex == 3)
		{
			renderTextureState = "Specular";
		}
		else if (gScrrenTextureIndex == 4)
		{
            renderTextureState = "Final";
		}

		glfwSetWindowTitle(window, ("LearnOpenGL    Render:" + renderTextureState).c_str());


		// per-frame time logic
		// --------------------
		float currentFrame = static_cast<float>(glfwGetTime());
		deltaTime = currentFrame - lastFrame;
		lastFrame = currentFrame;

		// input
		// -----
		processInput(window);

		// 1.渲染 G-Buffer 数据
		glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
		glm::mat4 view = camera.GetViewMatrix();
		glm::mat4 model = glm::mat4(1.0f);
		gBufferShader.use();
		gBufferShader.setMat4("projection", projection);
		gBufferShader.setMat4("view", view);
		for (unsigned int i = 0; i < objectPositions.size(); i++)
		{
			model = glm::mat4(1.0f);
			model = glm::translate(model, objectPositions[i]);
			model = glm::scale(model, glm::vec3(0.5f));
			gBufferShader.setMat4("model", model);
			backpack.Draw(gBufferShader);
		}
		glBindFramebuffer(GL_FRAMEBUFFER, 0);

		// 2.光照处理阶段
        glBindFramebuffer(GL_FRAMEBUFFER, lightingPassFBO);
		lightingPassShader.use();
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, gPosition);
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, gNormal);
		glActiveTexture(GL_TEXTURE2);
		glBindTexture(GL_TEXTURE_2D, gAlbedoSpec);
		lightingPassShader.setVec3("viewPos", camera.Position);
		renderQuad();
		glBindFramebuffer(GL_FRAMEBUFFER, 0);

		// 3.将数据渲染到屏幕上
		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        screenShader.use();
		glActiveTexture(GL_TEXTURE0);
		unsigned int renderTextureIndex = 0;
		switch (gScrrenTextureIndex)
		{
		case 0:
			renderTextureIndex = gPosition;
			break;
		case 1:
			renderTextureIndex = gNormal;
			break;
		case 2:
			renderTextureIndex = gAlbedoSpec;
			break;
		case 3:
			renderTextureIndex = gAlbedoSpec;
			bRenderSpecular = true;
			break;
		case 4:
			renderTextureIndex = lightingPassColorBuffer;
			break;

		}
		glBindTexture(GL_TEXTURE_2D, renderTextureIndex);
        screenShader.setBool("bRenderSpecular", bRenderSpecular);
		renderQuad();
		bRenderSpecular = false;

		// 3.5 复制G-Buffer深度缓冲区数据到默认深度缓冲区
		// 绑定读取和写入帧缓冲
		glBindFramebuffer(GL_READ_FRAMEBUFFER, gBuffer);        // 源：G-Buffer 的帧缓冲
		glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);             // 目标：默认帧缓冲

		// 复制深度缓冲数据
		glBlitFramebuffer(
			0, 0, SCR_WIDTH, SCR_HEIGHT,                        // 源区域（全屏）
			0, 0, SCR_WIDTH, SCR_HEIGHT,                        // 目标区域（全屏）
			GL_DEPTH_BUFFER_BIT,                                // 复制深度缓冲
			GL_NEAREST                                          // 插值方式（深度数据无需插值）
		);
		glBindFramebuffer(GL_FRAMEBUFFER, 0);

		// 4.绘制光源立方体
		// 使用正向渲染绘制光源立方体（常规渲染流程）
		lightBoxShader.use();
		lightBoxShader.setMat4("projection", projection);  // 传递投影矩阵
		lightBoxShader.setMat4("view", view);              // 传递视图矩阵
		for (unsigned int i = 0; i < lightPositions.size(); i++)
		{
			// 构建模型矩阵（平移+缩放）
			glm::mat4 model = glm::mat4(1.0f);
			model = glm::translate(model, lightPositions[i]); // 定位至光源坐标
			model = glm::scale(model, glm::vec3(0.25f));      // 缩小立方体尺寸
			lightBoxShader.setMat4("model", model);           // 传递模型矩阵
			lightBoxShader.setVec3("lightColor", lightColors[i]); // 设置光源颜色
			renderCube(); // 渲染立方体基元
		}

		// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
		// -------------------------------------------------------------------------------
		glfwSwapBuffers(window);
		glfwPollEvents();
	}

	// optional: de-allocate all resources once they've outlived their purpose:
	// ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteBuffers(1, &cubeVBO);
    glDeleteVertexArrays(1, &quadVAO);
    glDeleteBuffers(1, &quadVBO);
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteBuffers(1, &cubeVBO);

	glfwTerminate();
	return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow* window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
	{
		glfwSetWindowShouldClose(window, true);
	}
	else if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::FORWARD, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::BACKWARD, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::LEFT, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::RIGHT, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_Q) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::UP, deltaTime);
	else if (glfwGetKey(window, GLFW_KEY_E) == GLFW_PRESS)
		camera.ProcessKeyboard(Camera_Movement::DOWN, deltaTime);

	if (glfwGetKey(window, GLFW_KEY_RIGHT) == GLFW_PRESS && !bToggleGBufferKeyPressed)
	{
		gScrrenTextureIndex = (gScrrenTextureIndex + 1) % 5;
		bToggleGBufferKeyPressed = true;
	}
    if (glfwGetKey(window, GLFW_KEY_RIGHT) == GLFW_RELEASE)
	{
		bToggleGBufferKeyPressed = false;
	}

	if (glfwGetKey(window, GLFW_KEY_P) == GLFW_PRESS)
	{
		std::cout << "Position: " << camera.Position.x << ", " << camera.Position.y << ", " << camera.Position.z << "" <<std::endl;
		std::cout << "Rotation: " << camera.Yaw << ", " << camera.Pitch << "" << std::endl;
	}
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	// make sure the viewport matches the new window dimensions; note that width and 
	// height will be significantly larger than specified on retina displays.
	glViewport(0, 0, width, height);
}

void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
	static bool firstMouse = true;
	if (firstMouse) // 这个bool变量初始时是设定为true的
	{
		lastX = xpos;
		lastY = ypos;
		firstMouse = false;
	}

	float xoffset = xpos - lastX;
	float yoffset = lastY - ypos; // 注意这里是相反的，因为y坐标是从底部往顶部依次增大的
	lastX = xpos;
	lastY = ypos;

	camera.ProcessMouseMovement(xoffset, yoffset);
}

void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
	camera.ProcessMouseScroll(yoffset);
}

unsigned int loadTexture(char const* path, bool gammaCorrection, bool bFlipV)
{
	unsigned int textureID;
	glGenTextures(1, &textureID);

	int width, height, nrComponents;
	if (bFlipV)
	{
        stbi_set_flip_vertically_on_load(true);
	}
	unsigned char* data = stbi_load(path, &width, &height, &nrComponents, 0);
	if (data)
	{
		GLenum internalFormat;
		GLenum dataFormat;
		if (nrComponents == 1)
		{
			internalFormat = dataFormat = GL_RED;
		}
		else if (nrComponents == 3)
		{
			internalFormat = gammaCorrection ? GL_SRGB : GL_RGB;
			dataFormat = GL_RGB;
		}
		else if (nrComponents == 4)
		{
			internalFormat = gammaCorrection ? GL_SRGB_ALPHA : GL_RGBA;
			dataFormat = GL_RGBA;
		}

		glBindTexture(GL_TEXTURE_2D, textureID);
		glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, dataFormat, GL_UNSIGNED_BYTE, data);
		glGenerateMipmap(GL_TEXTURE_2D);

		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

		stbi_image_free(data);
	}
	else
	{
		std::cout << "Texture failed to load at path: " << path << std::endl;
		stbi_image_free(data);
	}

	stbi_set_flip_vertically_on_load(false);

	return textureID;
}

void renderCube()
{
	// initialize (if necessary)
	if (cubeVAO == 0)
	{
		float vertices[] = 
		{
			// back face
			-1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
			 1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
			 1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 0.0f, // bottom-right         
			 1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
			-1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
			-1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 1.0f, // top-left
			// front face
			-1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
			 1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 0.0f, // bottom-right
			 1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
			 1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
			-1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 1.0f, // top-left
			-1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
			// left face
			-1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
			-1.0f,  1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-left
			-1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
			-1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
			-1.0f, -1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-right
			-1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
			// right face
			 1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
			 1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
			 1.0f,  1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-right         
			 1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
			 1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
			 1.0f, -1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-left     
			 // bottom face
			 -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
			  1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 1.0f, // top-left
			  1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
			  1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
			 -1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 0.0f, // bottom-right
			 -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
			 // top face
			 -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
			  1.0f,  1.0f , 1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
			  1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 1.0f, // top-right     
			  1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
			 -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
			 -1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 0.0f  // bottom-left        
		};
		glGenVertexArrays(1, &cubeVAO);
		glGenBuffers(1, &cubeVBO);
		// fill buffer
		glBindBuffer(GL_ARRAY_BUFFER, cubeVBO);
		glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
		// link vertex attributes
		glBindVertexArray(cubeVAO);
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
		glEnableVertexAttribArray(2);
		glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
		glBindBuffer(GL_ARRAY_BUFFER, 0);
		glBindVertexArray(0);
	}
	// render Cube
	glBindVertexArray(cubeVAO);
	glDrawArrays(GL_TRIANGLES, 0, 36);
	glBindVertexArray(0);
}

void renderQuad()
{
	if (quadVAO == 0)
	{
		float quadVertices[] = 
		{
			// positions        // texture Coords
			-1.0f,  1.0f, 0.0f, 0.0f, 1.0f,
			-1.0f, -1.0f, 0.0f, 0.0f, 0.0f,
			 1.0f,  1.0f, 0.0f, 1.0f, 1.0f,
			 1.0f, -1.0f, 0.0f, 1.0f, 0.0f,
		};
		// setup plane VAO
		glGenVertexArrays(1, &quadVAO);
		glGenBuffers(1, &quadVBO);
		glBindVertexArray(quadVAO);
		glBindBuffer(GL_ARRAY_BUFFER, quadVBO);
		glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), &quadVertices, GL_STATIC_DRAW);
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
	}
	glBindVertexArray(quadVAO);
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
	glBindVertexArray(0);
}
